whatsis?

I have adopted a pile of books to sort through, mostly science and medical texts from the mid 1800’s-early 1900’s, some leatherbound, some with marbled text blocks, some nothing special. However, about half of them unfortunately have an odd remainder-type mark which I am at a loss to describe accurately. It is an odd shaped mark, but as these books were probably not remaindered in the current sense, I am not sure what to call it when describing the books. A discard mark? There is no evidence of ex-library markings or pockets so I would hesitate to call it a discard in that sense of the word. If anyone wants to take a look and give an ID or provide my brain a creative descriptive jump start, feel free and much appreciated.email me at info at ravenroostbooks dot com